| In recent years,with the development of society and economy,people’s living standards have been continuously improved,and the demand for automobiles has been increasing.The high-performance vehicle-mounted radar system and traffic monitoring radar system have very important practical significance and prospects.Millimeter-wave radar antennas have also become a hot research topic,facing challenges such as low gain,narrow frequency band,large size,and high cost.This article has conducted in-depth research around the broadband millimeter-wave vehicle radar antenna array.The main research work and results are as follows:First,based on the equivalent circuit method of the substrate integrated waveguide(SIW)and the Elliott equation,a twelve-element center-fed SIW slot array antenna operating at76～81 GHz was designed.The machine-learning method was used to establish an agent model,combined with differential evolution algorithm and HFSS,the maximum sidelobe level of the antenna array in the pitch plane of 76～81 GHz is optimized below-21 dB,and the SIW-WR10 transition structure is designed for the waveguide test method of the antenna.The measured results show that the gain at center frequency of 79 GHz is 9.9 dBi,and the SLL in the E plane at 79 Ghz is-19.3 dB.Then,two different structures of SIW to microstrip transition structure are designed to achieve vertical transmission in multilayer circuit boards.The simulation results show that the insertion loss of the two structures at center frequency of 79 GHz is 1.5 dB and 1.23 dB,respectively.The working bandwidth of the antenna in the multilayer board environment covers 76～81 GHz,the gain in the frequency band is greater than 10 dBi,and the side lobe is lower than-18.4 dB.In order to improve the gain and the consistency of direction pattern,a sixteen-element SIW slot array antenna was designed.The machine-learning-assisted optimization method with target threshold was used to optimize the antenna.Under the constraint of the gain,The maximum sidelobe level of the inner pitch plane in the band of76～81 GHz is optimized below-20 dB.The antenna array has a gain of 14.6 dBi at center frequency of 79 GHz,and the pattern meets the requirements of millimeter-wave vehicle radar.This method can avoid the over-optimization of a single target while searching for the optimal value.The result is more accurate and more suitable for the design of broadband millimeter-wave automotive radar antennas.Finally,the bandwidth advantage of the proximity-coupled feeding method is introduced into the series-fed microstrip array.Based on the patch element width tapering method,a12-element series proximity-coupled fed microstrip patch antenna array operats in the band of76～81 GHz is designed.Open branches are connected in parallel at specific positions of the transmission line to adjust the matching.Using machine-learning-assisted multi-objective optimization method with additional feature and target threshold,combined with the electromagnetic full-wave simulation software HFSS,the maximum sidelobe level of the antenna array in the pitch plane of 76～81 GHz is optimized below-19.2 dB.This series proximity-coupled fed microstrip patch antenna array can significantly improve broadband performance without increasing its complexity,size and cost.In order to measure the antenna array,a Microstrip-Finline-WR12 transition structure and metal waveguide structure which are suitable for thin substrates are designed.The measured results show that the antenna array has a gain of 12.1 dBi at frequency of 77 GHz. |
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